Electrostimulation can be delivered to a heart, such as to trigger or to spatially coordinate a responsive cardiac depolarization and accompanying heart contraction. An implantable or other ambulatory cardiac function management device, such as a pacer, a cardioverter, a defibrillator, a cardiac contractility modulation (CCM) or a cardiac resynchronization therapy (CRT) device can be configured to include capability for monitoring cardiovascular function or for generating or providing such stimulation to the heart, such as for triggering or spatially coordinating responsive heart contractions. Such electrostimulations can be delivered via two or more electrodes. For example, such electrodes can include one or more electrodes that can be located at or near the distal end of one or more implantable leadwires, which can be connected to an implantable cardiac function management device. Such electrodes can also include one or more electrodes located at the implantable cardiac function management device.
Electrostimulation can be either cathodal or anodal, or a combination of anodal and cathodal. In cathodal stimulation, a more negative electrode (e.g., in an arrangement of electrodes) “captures” contractile cardiac tissue to trigger the resulting cardiac depolarization and accompanying heart contraction. In anodal stimulation, a more positive electrode (e.g., in an arrangement of electrodes) triggers the resulting cardiac depolarization and accompanying heart contraction. Various factors can influence whether anodal or cathodal stimulation occurs. For example, relative electrode size of an anode vs. a cathode can determine whether anodal, cathodal, or a combination of anodal and cathodal stimulation occurs. An electrode having a smaller surface area can have a greater current density through nearby tissue than a larger electrode. Greater current density can lower the threshold amount of energy needed to evoke a resulting cardiac depolarization and accompanying heart contraction.
The threshold amount of energy needed to evoke a resulting cardiac depolarization and accompanying heart contraction can differ for anodal stimulation vs. cathodal stimulation. Typically, for a selected electrode, the anodal stimulation threshold is higher than the electrode's cathodal stimulation threshold. Discriminating between anodal stimulation and cathodal stimulation during the delivery of an electrostimulation therapy may be useful in determining an optimal pacing configuration. For example, in some cases, it may be that the anodal threshold is lower than the cathodal electrode for a particular electrode site.